In many industrial environments, products are processed and/or stored in tanks prior to their disposition. Examples of such use of storage tanks include the batch processing of foods, beverages, or pharmaceuticals. In these industries, one must be able to reliably determine the amount of contents stored within a tank at any given time. This determination may be made visually or through the use of apparatus that gauges the level of such contents. In many instances, the structural components of the tanks themselves prevent any sort of visual determination of the present level of the contents. For example, many tanks are composed of steel or other nontransparent materials and, therefore, any visual inspection of the content level of such tanks would involve manually opening the tank. Any opening of a tank presents the potential problem of contaminating the contents with microorganisms or other foreign substances. This problem is especially pronounced in tank applications which need to remain sanitary, such as the batch processing of foods and/or pharmaceuticals. Aside from contamination, visual inspection of content levels lacks accuracy and would be time consuming. In order to avoid these problems, level sensing gauges are used to measure content levels in storage and processing tanks.
There are several types of level sensing gauges. Examples include those that use radar transmitters, or ultrasonic waves. Regardless of the gauge's method of operation, there is a need for accuracy in level measurement. A high degree of accuracy has been achieved by the use of level sensing gauges which monitor content levels by transmitting microwave pulses from an antenna toward the surface of the tank contents. These pulses are reflected from the contents and back to the antenna. In most applications a waveguide, which is generally rod-shaped, is used to direct the transmitted pulse to the tank contents and the reflected echo back to the antenna of the level sensing gauge. Other radar gauges use a continuous wave rather than pulses.
Radar sensors are suitable for liquids, solids, powders, granules, dust, corrosive steam and vapors, regardless of the media characteristics, environment, low and high pressures or temperatures.
Radar signals are unaffected by noise, by extreme air turbulence, such as during pneumatic filling, or by fluctuations in dielectric constant above a nominal minimum value, density, or conductivity. Even liquids having highly agitated surfaces or gas bubbles are usually reliably measured. Gas layering such as that produced by solvents or gases has virtually no adverse effect.
Although the use of radar and pulses has served in increase the accuracy of level sensing gauges, they are still susceptible to decreased precision. For instance, a problem concerning interference with radar signals has arisen due to the structure of the level sensing gauges themselves and becomes especially pronounced when the gauges are combined with their operation in a storage tank. In general, a level sensing gauge consists of a housing which encloses the components of the transmitter and the antenna of the gauge. The antenna both transmits and receives microwave pulses of radar, which travel down a waveguide and are subsequently reflected off the contents of the tank and returned to the antenna via the waveguide. Objects in close proximity to the antenna may potentially disrupt the microwave pulses of radar thereby resulting in false echoes and imprecise readings. One such object is the roof and/or body of the storage tank to which the level sensing gauge is attached. The very configuration of the level sensing gauge as attached to the storage tank thus facilitates the disruption of the radar pulses.
In securing a level sensing gauge to a storage tank, a hole is first cut into the body of the tank, generally the roof. Next, a collar will be welded to the tank surrounding this hole. The level sensing gauge is then inserted through the collar and hole into the tank with the antenna and waveguide aligned to reflect microwave pulses off the surface of the contents in the tank. The level sensing gauge is then clamped to the collar of the tank. This configuration of the level sensing gauge attached to the roof of a storage tank results in the antenna being in close proximity to the roof of the storage tank. This location disrupts both the transmittal and reception of microwaves thus decreasing the accuracy of level measurement.
Another problem created by methods of attachment of level sensing gauges to storage tanks is the potential for contamination which was previously discussed. During attachment, the exterior of the housing which constitutes the mounting for the level sensing gauge is generally threaded. The attachment of the housing to the collar of the storage tank involves multiple components. To aid in the sanitary sealing of the gauge to the tank, gaskets are interposed between the various components of the mounting and collar. In this method of attachment there exist several potential locations to entrap microorganisms or other substances foreign to the contents of the tank which cannot readily be cleaned. Therefore, these methods of attachment are not adequate for those applications which require a sanitary seal.
Accordingly, and in view of the above background, there is need for a level sensing gauge which is sanitarily sealable to a storage tank to prevent the ingress of microorganisms and other contaminants to the contents therein. Further, it is desirable that as the level sensing gauge is sanitarily sealed during attachment to a storage tank its antenna is positioned so as to eliminate any interference with the microwave radar pulses by the body of the tank.